Download 1 INTERNATIONAL LITHOSPHERE PROGRAM (ILP) Proposal for

May 20, 2015
INTERNATIONAL LITHOSPHERE PROGRAM (ILP)
Proposal for new Task Force: 2015-2019
“FATE OF THE SUBDUCTED CONTINENTAL LITHOSPHERE: INSIGHT
THROUGH ANALYTICAL MINERALOGY AND MICROSTRUCTURES”
Chair person: Larissa Dobrzhinetskaya, University of California at Riverside, USA, [email protected]
Coordinator: Junfeng Zhang, The China University of Geoscience, Wuhan, China, [email protected]
Scientific rationale and objectives. The subduction of the continental lithosphere into Earth’s
interior leads to dramatic changes in the dynamics of the mantle as well as seismic and volcanic
activities at the convergent systems. The geological processes that resulted from the continental
crust-mantle interaction are complex and diverse and may evolve into different scenarios. One
well-accepted model is that the Si-rich continental material keeps subducting into the mid-upper
mantle where it is subjected to partial melting, thus causing volcanic events. However,
experimental studies have shown that a part of the crustal material that delaminated and avoided
melting may be modified to become denser than surrounding mantle. The latter “sunk down” into
the mantle transition zone, and possibly the lower mantle, to stagnate for a long geological time.
High-pressure experiments showed that the “average continental crust” will be denser than the
surrounding mantle by ~0.20 g/cm3 at depth ~410 km, whereas with increasing pressure at depth
~660 km, the “average continental crust” becomes slightly less dense then mantle rocks at
~0.15g/cm3 (Nishiyama et al., 2005; Dobrzhinetskaya & Green, 2006). Therefore, the 660-km seismic
discontinuity zone can be considered a place where continental materials can stagnate. Because
samples of rocks at that depth are not directly accessible, studies of small fragments such as
xenocrysts, xenoliths, or geochemical and mineralogical anomalies containing records of a crustmantle interaction are first-order questions for modern geosciences.
It is now believed that only very small fragments of the continental materials of a specific
composition will reach 660-km seismic discontinuity and stagnate there, as well as in the
neighboring horizons of the lower mantle. These fragments will eventually be assimilated into the
mantle minerals, or preserved as tiny xenocrysts within them. Through the mantle convection, the
relicts or remnants of the modified crustal materials are re-distributed within different geological
settings and eventually may be delivered to the Earth surface through deep volcanisms, mantle
plumes, tectonic exhumations, etc (e.g. Dobrzhinetskaya et al., 2014; Sumino et al.2011).
The minerals and microstructures indicative of ultrahigh pressure (UHP) conditions and phase
transformations in a variety of tectonic environments represent a new insight into an
understanding of the fate of the subducted continental lithosphere. The number of tectonic
settings in which new UHP minerals have been discovered is no longer limited only by orogenic
belts. During the last five years, the numbers continue to grow and an interdisciplinary approach
is required to understand how the fragments of the continental lithosphere are “amalgamated”
with the mantle.
We propose a new Task Force project to make breakthroughs in studying integrated
processes that lead to the mineralogical-geochemical assimilations of the continental lithosphere
that was subducted to the deep Earth’s interior. These studies will provide a foundation for
understanding first-order problems that will advance modeling of the larger scale processes
related to plate tectonics and deep geophysics. Multidisciplinary in nature, the project will
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integrate efforts of geologists from the U.S., China, Germany, Israel, Bulgaria, S. Korea, Canada,
and Russia. The new Task Force will have also a strong intellectual connection to wellestablished interdisciplinary organizations such as the International geological Correlation
(IGCP), the Consortium of Materials Research in the Earth Sciences (COMPRES), the Deep
Carbon Observatory (DCO), and The Asian Network in Deep Earth Mineralogy (TANDEM).
Together, we will promote the advancement of experimental and computational studies on physical
properties, structures, dynamics, and evolution of the Earth’s deep interior.
GOALS AND SCOPS OF THE NEW TASK FORCE
Goals. The new Task Force project will be focused on the wide range of phenomena and
processes that help to understand the fate of the continental lithosphere subducted to the deep
Earth’s interior. The project would attempt to answer first-order fundamental questions in regard
to the depth at which the subducted continental lithosphere was stagnated, how its fragments
could be recognized if the continental rocks are modified at high pressure and high temperatures,
and if the relict fragments occur within non-traditional geological environments. The project
outlines frontier questions of modern geology, geodynamics, and geophysics and solutions that
require integration of new experimental technologies, achievements in modern geophysics and
mineral physics, state-of-the-art analytical instruments, and modern synchrotron facilities.
Analytical mineralogy in combination with petrology and geochemistry, mineral structures, phase
transformations, rheology, microstructures, and modeling of different scales will be instrumental
in understanding the mantle geodynamics behind the ultra-deep subduction of the continental
lithosphere.
The goal of the project fits the mission of the ILP, which promotes interdisciplinary studies
to build larger observational and experimental modeling platforms for understanding the mantle
dynamics through the fate of the subducted lithosphere as well as its deformational and
mineralogical-geochemical evolution.
Scope #1. Light elements as indicators of the continental lithosphere assimilated into the
mantle. Light elements such as carbon, nitrogen, hydrogen, oxygen and others, including their
volatile derivates (e.g., CO2, CH4, N2O, C2F4 and others) can be sequestrated by mantle rocks and
minerals due to the assimilation of the continental lithosphere into the Earth’s mantle. On a larger
scale, these elements, being chemically bonded in the structure of high-pressure minerals, may
drastically change the mantle’s physical properties followed by formation of some regional
seismic discontinuities, similar to that described in the Alps (Nita et al., 2011). On the other hand,
during decompression of high-pressure phases due to the uplift through the mantle convection and
tectonic exhumations, the light elements can be deliberated and they may lower solidus
temperatures, viscosities, and plastic deformation features of the bulk rocks. Moreover, the light
elements’ dissolution into the grain-boundary melts may promote more rapid mantle convection,
return flows, mantle plume formations, and mantle de-volatilization. A better understanding of
these phenomena requires high-resolution analytical studies of mineral microstructures and small
inclusions of liquid and solid matter trapped by high-pressure minerals during crystallization.
Scope #2. Geophysical aspects of carbon and nitrogen. Both the elements of carbon and
nitrogen are considered hypothetical candidates that account for the density deficit of the Earth’s
core. The reason for such a hypothesis is that seismic S-waves travel through the Fe-Ni inner core
of the Earth at about half the speed expected for most Fe-Ni alloys measured under relevant
pressure in a laboratory setting. Contrary to the traditional concept that the gap in seismic S-wave
velocities can be attributed to the presence of liquid in the inner core, more recent models
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consider that light elements, including C, N, S, Si, O and H (or one of all), should be added to the
existing Fe-Ni compositional model of the inner core to satisfy the seismic-velocities record (e.g.
Chen et al., 2014). Studies of carbide and nitride group minerals in the natural environment as well
as in a laboratory will help to determine what kind of light elements better fit S-wave velocities
during their travel through the Earth’s inner core.
Scope #3. Isotope chemistry of C and N as an indicator of the fate of the subducted
continental lithosphere. Since the range of δ13C and δ15N measured in many geological
complexes allow researchers to distinguish (with some degree of approximation) the “crustal”
(shallow) reservoirs from their mantle counterparts, both elements are important for a search of
the continental lithosphere relicts that reside within rocks of the Earth’s mantle. For
understanding the assimilation of crustal C and N into the mantle by creating new ultra-high
pressure minerals or through incorporation into well-known mantle high-pressure phases, we need
to observe the natural minerals and to continue experimental modeling of conditions leading to
the mixing of crustal and mantle materials. Moreover, consideration of the global carbon and
nitrogen cycles has traditionally been focused primarily on near-surface, low-temperature
reactions. This knowledge has been limited by the assumption that the oceans, atmosphere, and
shallow surface and oceanic sediments represent a “closed system” with respect to biological
carbon and “continental” nitrogen. However, new findings of carbides and nitrides in different
terrestrial sources have changed this paradigm and demanded a reappraisal of the “fluctuating”
role of carbon, nitrogen, and other volatiles as a flux that could trigger chemical reactions and
control light elements in regards to (1) partition between solid and melt, and (2) strengthen
mineral plastic flows in the deep Earth.
Scope #4. A new focus on studies of terrestrial minerals of the carbide and nitride groups.
Although carbides and nitrides are accessory minerals, their presence within rocks of the mantle
environments has not been fully appreciated until the recent discoveries of moissanite (SiC) and
cBN within a mantle section of ophiolite formation (Yang et al., 2007; Dobrzhinetskaya et al.,
2014). Both groups of minerals have a lot to offer in understanding the deep mantle’s state of
oxidation, and if carbon and nitrogen constituents in both groups belong to only crustal, or
mantle, or mixed reservoirs. Carbides and nitrides may be formed only in environments with a
high deficiency of oxygen, and pressure and temperature are considered the varying factors.
Moissanite (SiC) is traditionally considered a high-pressure mineral whose formation requires
extremely reduced conditions of 4.5–6 log units below the IW fugacity buffer. Most moissanites
are found as inclusions in diamonds and as xenocrysts in kimberlites, in ophiolitic chromitites,
peridotites, and in metasomatic rocks with references to their mantle origins (for review see:
Shirayev et al., 2013). We will continue to study in detail one of the new moissanite deposits in
Israel that is connected to interplate alkali basalts magmatism (Mukhin et al., 2015).
Qingsongite (cubic BN). Our recent discovery of a new mineral qingsongite, cubic BN
(sphalerite/zincblende structure), in the mantle section of the Tibetan ophiolite, showed that this
mineral has a mixed “parentage”—boron has a crustal origin, whereas nitrogen (δ15N = ‒10.4 ± 3
‰) is most likely from the mantle (Dobrzhinetskaya et al., 2014). This mineral was crystallized
under highly reducing conditions accompanied by high pressure (10–15 GPa) and high
temperature (~1300 °C) at the depth > 250–300 km. Such a combination is not a surprise for a
crustal material that was, at least once, deeply subducted and then exhumed back to shallow Earth
levels. The occurrences of cBN in association with osbornite (TiN), coesite pseudomorphs of
stishovite, moissanite and coesite exsolution lamellae in chromium spinel in the Tibetan ophiolite
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mantle section, have important implications for understanding the assimilation processes of the
continental material into the mantle (e.g. Dobrzhinetskaya et al., 2009; Yang et al., 2007).
Scope #5. Experimental exploration of the stability fields of carbides and nitrides. Both of
the SiC and cBN compounds were first synthesized in laboratories and only later discovered as
minerals in the Earth’s geological formations. SiC and BN are extremely valuable technological
materials for electronics and ceramics and were industrially produced at a wide range of high
temperatures (1200–2500 oC). Experiments on both materials at high pressures are very rare,
although it is known that some polytypes of SiC remain stable at pressures up to 100 GPa
(Yoshida et al., 1983), while cBN is stable at pressure > 22 GPa. Recent experiments (Schmidt et
al., 2014) have shown that SiC can be formed from an ultra-reduced fluid at T = 700–800 oC, and
its formation in experiments does not reflect any equilibrium with the surrounding host rocks. The
new experimental programs with diamond-anvil cell, multianvil, and piston-cylinder apparatus
techniques will address this controversy in the future.
Scope#6. The use of state-of-the-art microanalytical techniques and synchrotron-related
technologies for mineralogical studies. The Task Force will continue to promote advanced
electron microscopy, synchrotron-related X-Rays, and other spectroscopic methods. The growing
field of nanoscale geoscience has already demonstrated the importance of establishing a profound
correlation between results obtained with synchrotron light sources, focused ion beam (FIB),
high-resolution transmission scanning electron microscopy, secondary ion-mass spectrometry
(nano-SIMS) and other techniques. Our new Task Force will promote knowledge and explain the
scientific importance of these instruments and techniques to students and colleagues through
collaboration with the above mentioned interdisciplinary organizations.
Administration of the Project. The new Task Force office will be established at the University
of California at Riverside. A website will be developed that describes the project and make it
available to the scientific community. Meetings among the active members will be held once a
year during official large conferences and workshops. Between the meetings, the chairperson and
the coordinator of the project will communicate with active members and ILP administration via
e-mail, fax, and telephone.
Short - and Long-Term Activities:
1. Organizing workshops and special sessions at international meetings for scientific
exchanges and discussion, and encouraging participations of the graduate students.
2. Publish new developments and achievements in Books, Special Volumes, and
international scientific journals.
3. Circulating information by setting up an electronic mailing list and a webpage.
Strengthening the relationship with other programs such as IGCP, COMPRES, DCO and
TANDEM in order to better understand continental and mantle dynamics.
REFERENCES
Chen et al., 2014, PNAS 111:17755–17758; Dobrzhinetskaya & Green, 2007 J. Met.Geol. 25:8396; Dobrzhinetskaya et al., 2009, PNAS 106:19233-19238; Dobrzhinetskaya et al., 2014, Am.
Miner. 99:764-772; Mukhin et al., 2015, Goldschmidt Conf., Abstracts; Nita et al., 2011, Phys.
Earth & Planet. Inter. 206-207:1-15; Nishiyama et al., 2005, Phys. Chem. Minerals 32:627–637;
Shirayev et al., 2011, Lithos 123:152-164; Schmidt et al., 2014, Progr. Earth Planet. 1:27; Yang
et al., 2007, Geology, 35:875-878.
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CURRICULUM VITAE
LARISSA F. DOBRZHINETSKAYA
University of California at Riverside, USA
[email protected]; tel:1-951-827-2028
EDUCATION
Doctor of Science (geology/mineralogy). Supreme Commission of Education, Moscow, 1990
Ph.D (mineralogy/geophysics) Institute of Geology & Geochronology, S.-Petersburg, Russia, 1982
Diploma (M.S.-B.S. in structural geology) S.-Petersburg University, Russia, 1978
ACADEMIC POSITIONS:
1998-present – Professor (Step VI), Research Geophysicist, Institute of Geophysics and Planetary
Physics; Department of Earth Sciences, UC Riverside
2004-2005, International Scholar – JSPS Fellow, Waseda University, Tokyo, Japan
1998-1999, Center for Materials Science, Los Alamos National Laboratory, New Mexico
1993-1998, Research Geophysicist, Institute of Geophysics and Planetary Physics, UCR
1992-1993, Senior scientist. Geological Survey of Norway, Trondheim, Norway
1991-1992, Lecturer. Faculty of Geology. Moscow University, Russia
1984-1992, Leading Scientist. Institute of the Lithosphere. Russia
1978-1984, Leading Scientist, Scientist, Junior Researcher, Institute of Physics of the Earth,
GUEST LECTURES given at following institutions (last 5 years):
Annenberg Educational Center, USA (2014), Carnegie Institution of Washington – Geophysical
Laboratory (2013); University of British Columbia, Canada (2013); University of Colorado,
Boulder, USA (2012); Syracuse University, New York, USA (2012); Gemological Institute of
America (2011); Mineralogical Society of South California, Pasadena, CA (2011); Charles
University, Czech Republic, Prague (2010), China University of Geosciencies, Wuhan (2010).
HONORS and FELLOWSHIPS
Fellow of Mineralogical Society of America
Fellow of American Association for Advancement in Science
Fellow of Geological Society of America
Fellow of Japanese Society for Promotion in Science
Distinguished Researcher Award, 2001, UC Riverside
Recipient of Fellowship from the Los Alamos National Laboratory, 1999
Recipient of Fellowship from Norwegian Council for Scientific and Industrial Research, 1993
Goldschmidt’s Lecture Series (GLS), Invited Lecture, Trondheim, Norway, 1996
PROFESSIONAL ACTIVITY:
Editorial Board member: Journal of Metamorphic Geology, Journal of Earth Sciences, Springer.
Editor of Books: 1.Ultrahigh Pressure Metamorphism: 25 year after discovery of coesite and
diamonds in collisional belts. Elsevier, 2011, pp500. 2. Advances in high-pressure technology for
geophysical applications, Elsevier, 2005, pp.511.
Author of the text Book: Minerals and Human Health. Cognella, 2015, pp.475.
Invited Editor for Spec.Volumes: Gondwana Research, 2011; J. Earth Sciences, 2010; J. Met.
Geol., 2011, 2009, 2006; Lithos, 2009, 2007.
Member of the MSA and GSA Committees of the “Best Student in Research” (2007-2012).
Chair of Education and Outreach Committee, AGU, 2009-2010; member: 2004-2008.
Chair of Task Force IV, International Lithosphere Program, 2010-2014; 2005-2009.
Vice-chair of the Mineral Equilibrium Group, IMA (2010-2014).
CURRICULUM VITAE
JUNFENG ZHANG
School of Earth Sciences
China University of Geosciences
Wuhan, Hebei 430074
Phone: (86)13377899448
Fax: (86)67883001
Email: [email protected]
EDUCATION:
2001-2005
1997-2000
1993-1997
Ph.D., Department of Earth Sciences, University of California, Riverside,
USA, Supervisor: Dr. Harry W. Green II
M.S., School of Earth Sciences, China University of Geosciences at Wuhan,
P.R. China
B.S., School of Earth Sciences, China University of Geosciences at Wuhan,
P.R. China
ACADEMIC POSITIONS:
2014.05-present
2013.05-present
2008-present
2008-2013
2007-2008
2006-2008
Associate Dean, School of Earth Sciences, China University of Geosciences,
Wuhan
Chairman, Department of Structural Geology, School of Earth Sciences,
China University of Geosciences, Wuhan
Professor, School of Earth Sciences, China University of Geosciences
“Hubei Chutian Scholar” Professor, School of Earth Sciences, China
University of Geosciences
Associate Professor, School of Earth Sciences, China University of
Geosciences
Postdoctoral research fellow, Tectonophysics Laboratory, Department of
Earth Sciences, University of California at Riverside
SCIENTIFIC SERVICES:
2010-2014
2010-present
2012-present
2012-2013
2010-2011
Vice Chair, Task Force IV, International Lithosphere Program
Vice Director, Committee of Experimental Mineralogy, Petrology and
Geochemistry, Chinese Society of Mineralogy, Petrology and Geochemistry
Associate Editor-in-Chief, Journal of Earth Science
Guest editor, Gondwana Research special volume on HP/UHP terranes
Editor, Journal of Earth Science
PUBLICATIONS:
More than 33 peer-reviewed publications in international journals.